title: Plasma membrane phosphate transport and extracellular phosphate concentration in the regulation of cellular respiration in isolated perfused rat heart.
abstract: The role of extracellular Pi and transmembrane fluxes across the sarcolemma in the regulation of cellular respiration was studied in isolated Langendorff-perfused rat hearts. Extracellular phosphate did not significantly affect the oxygen consumption or cellular phosphorylation potential of the myocardium. K+-induced arrest was used to change the mechanical work load of the heart. Arresting the heart caused a rapid decrease in the unidirectional efflux of phosphate determined by in vitro prelabelling of the intracellular phosphate compounds with 32P and determining the specific radioactivity of the gamma-P of ATP, and the label appearance into the perfusion medium. At normal or elevated perfusate phosphate concentration there was a fairly slow net uptake of phosphate. The decrease in phosphate fluxes upon the K+-induced arrest was probably not due to a decrease in the transmembrane Na+ or K+ gradients because a further increase in the perfusate K+ concentration caused an increase in the K+ efflux to the levels observed in contracting hearts. The use of higher than normal concentrations of phosphate necessitated a lowering of the extracellular Ca2+ concentration, which caused a diminution of the oxygen consumption, accompanied by mitochondrial flavoprotein in the heart. This finding suggested that the extracellular Ca2+ concentration may be involved in the substrate level regulation of mitochondrial metabolism.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D005260:Female; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D010477:Perfusion; D010710:Phosphates / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010710:Phosphates; D004492:Edetic Acid; D002118:Calcium